Oncolytic virus-mediated p53 activation boosts the antitumor immunity of a p53-transduced dendritic cell vaccine

Dendritic cells (DCs) transduced with replication-deficient, wild-type human p53-expressing adenovirus Ad-p53 (Ad-p53 DCs) induce p53-targeting cytotoxic T lymphocytes (CTLs). However, the antitumor efficacy of Ad-p53 DCs is diminished by weak p53 immunogenicity in tumor cells and poor immune responses. We developed a p53-armed oncolytic adenovirus, OBP-702, to induce tumor-specific p53 expression and antitumor immune response, suggesting a role for OBP-702 in enhancing the antitumor efficacy of Ad-p53 DCs. The combined effect of Ad-p53 DCs and OBP-702 was investigated using murine colon cancer (CC) tumor models. Ad-p53 DCs were obtained by stimulating bone marrow-derived cells with granulocyte-macrophage colony-stimulating factor, interleukin-4, and Ad-p53. Subcutaneous tumor models of CT26 (p53 wild-type) and MC38 (p53 mutant-type) murine CC cell lines were used to evaluate the therapeutic potential of combination therapy in the terms of tumor growth, abscopal effect, antitumor immune response, and presentation of p53 peptides in tumor cells. Combination therapy with Ad-p53 DCs and OBP-702 significantly suppressed the growth of p53-intact CT26 tumors at treated and untreated sites by inducing tumor-infiltration of CD8+ CTLs and CD11c+ DCs. OBP-702-infected tumor cells presented human p53 epitopes in the context of major histocompatibility complex molecules, which were recognized by CTLs induced by Ad-p53 DCs. Combination therapy significantly suppressed the growth of p53-mutant MC38 tumors by activating the antitumor immune response. Our results suggest that OBP-702-mediated presentation of p53 epitopes on tumor cells enhances the antitumor efficacy of Ad-p53 DCs against murine CC tumors by attracting p53-targeting CTLs.